In short, we now use the renewable resources and ecological services of 1.5 Earths. If population and consumption trends increase at even the most conservative UN projections, Global Footprint Network’s data show we will need the equivalent of two Earths to meet our demands by 2030.

Look no further for a definition of “unsustainable.”

Today, August 20, marks the day we bust our ecological budget for 2013. In approximately seven months and 20 days, we have used all the renewable resources and ecological services that Earth was able to replenish this year. For the remaining of the year, we’re in overshoot.

You might be asking yourself: “I live in a wealthy country. Should I worry?” I think you should.

There is still plenty of nature on the planet, of course. The problem is, there’s not enough for everyone everywhere. Since we went into ecological overshoot in the early 1970s, we have been eating into our ecological capital. And as consumption and populations increase, there’s less to go around. In many parts of the world, more people are getting less.

Many high-income countries may not feel the sting right now. But all economies and societies — indeed, life itself — depend on access to ecological resources. Nations have spent natural capital as if it were infinite, but most haven’t bothered measuring it. They do not check on the oceans before deciding how much fish to take, or measure ecosystems’ sequestration capacity before emitting CO2. They don’t track the availability of wheat, rice, potatoes and other foods before paving over agricultural land.

And waste is something to throw out into the atmosphere, with little regard for the cost.

Our planet, however, has kept track of all that, and is exhausted for it. From today, we start spending beyond our means. We’re in ecological overshoot, two days earlier than last year.

On a global scale, this is extremely worrisome. For nations, it can be another step toward crisis. A country running an ecological deficit — that is, using more than it has — can fill some of the gap between the natural capital it has and what it requires, as long as it has the financial means to access outside resources. But this cost burden imposes economic pressure on the purchasing country. What happens when resources become more constrained and ever more costly?

We have only a 15 to 20-year window in which to turn the tide. Long-term economic health depends upon sound management of ecological resources. It is in governments’ own interests to deal with the reality of climate change and resource limits. Spending our natural capital without measuring its availability is foolhardy. I worry it might be a tragedy.

• Alessandro Galli is a Senior Scientist at Global Footprint Network, an international think-tank promoting a sustainable economy by advancing the use of the Ecological Footprint, a resource management tool that measures how much nature we have, how much we use and who uses what.